US Patent 6921253 Dual chamber micropump having checkvalves

A micropump has two chambers separated by an actuator for causing fluid to flow in the chambers. Each chamber is equipped with a ball that acts as a valve for allowing flow in a desired direction. The balls are heavier than the fluid being pumped, and reside at an interface between the chambers and passages feeding fluid into the chambers and provide a tight seal between the chambers and passages feeding the chambers when fluid pressure forces the fluid back toward the feeding passages.